This invention relates to a linkage for coupling a surface measuring instrument to an associated sensing probe, and particularly, to such a linkage which protects the probe from damaging hard strikes against the workpiece surface being evaluated.
"Profilometers" and "Surfometers" (registered trademarks) are used to provide an assessment of surface finish of workpieces, typically machined metal parts. These types of surface finish measuring devices have a probe with a stylus which is moved across the surface being evaluated. Vibrations of the stylus are recorded and evaluated by the instrument in a manner similar to operation of the conventional phonograph. The sensing stylus is very fragile and sensitive and care must be exercised to ensure that it is gently placed against the workpiece surface to avoid damage to the stylus which can occur if it forcefully impacts the workpiece surface.
One type of surface finish measuring device has a stationary housing containing the instrumentation with a link arm extending from the housing which is pivotable about a horizontal axis so that the arm may be raised to a vertical position when not in use. The arm can be rotated downwardly to place the stylus into contact with the workpiece surface for evaluation. The device then causes the stylus to move across the workpiece surface and the vibrations of the stylus are received and processed, and one or more values characterizing surface finish are outputted. For conventional surface finish measuring devices, the link arm is freely rotatable, and therefore care by the operator must be taken to gently rotate the arm so that the probe does not simply fall unimpeded against the workpiece surface. Unfortunately, such care is frequently not exercised by users necessitating replacement of the device's sensing probe.
In view of the foregoing, a need exists for a link arm assembly for surface finish measuring devices which prevents the probe from striking or "crashing" against the workpiece surface being evaluated.